Certain conditions in content distribution networks may cause subscribers to view content that was erroneously sent to them. This may include fully-viewable assets as well as partial frames inserted into the wrong session. Some conditions which may result in this problem are: (1) incorrect data written to a disk; (2) disks that fail to write data; (3) data read from an incorrect location; (4) erroneously streaming two programs to the same location; and (5) erroneously streaming a program to the wrong locations.
The problem may be mitigated by the use of a “content crawler”, which detects corruption and quarantines bad content from being accessed. Content may be checksummed when loaded on the video server. A server process continuously runs checksums across all content and compares to the original checksums. If the two checksums don't match, the content is quarantined (marked unreadable). It may take many hours to check all content on a system. Corruption may not be found for that period of time. That leaves a hole in the protection, a window after disk or volume corruption, and vectors unrelated to disk or volume corruption. Such vectors may include: (1) requesting the wrong content; (2) files being named incorrectly; (3) two streams sent to the same address; (4) a stream sent to the wrong set top box; and (5) packet corruption during network transmission and QAM (Quadrature Amplitude Modulation) processing.